1. Field of the Invention
The present invention relates to a method for connecting an optical fiber having a large Mode Field Diameter (MFD) to an optical fiber having a small MFD.
2. Related Background Art
High-speed communications utilizing a 1.55 xcexcm wavelength band via conventional optical transmission lines having a zero dispersion wavelength in a 1.3 xcexcm wavelength band have been put to practical use. In such a case, optical fibers having a negative dispersion at 1.55 xcexcm have been inserted, as dispersion compensating fibers, in the midsections of the optical transmission lines, so that the overall chromatic dispersion of the optical transmission lines can be reduced. MFDs of the dispersion compensating fibers are smaller than those of the optical fibers having a zero dispersion wavelength in a 1.3 xcexcm wavelength band.
In the case in which two optical fibers having different MFDs are connected together, connection loss increases if the optical fibers are merely bonded to each other. Accordingly, methods for reducing connection loss as disclosed in Japanese Patent Nos. 2618500 and 2951562 have been known in the art. According to the method disclosed in Japanese Patent No. 2618500, optical fibers having different core diameters are fusion-spliced together at first. Then, one of the optical fibers having a smaller core diameter is heated at a part near the spliced part, so that a dopant, contained in a core portion of the optical fiber, can be diffused and the difference of core diameters reduced.
Further, in Japanese Patent No. 2951562, is described a method for connecting a dispersion compensating fiber to a single mode optical fiber, with a low connection loss. According to this method, a dispersion compensating fiber is spliced to a single mode optical fiber via an intermediate optical fiber having MFD that is approximately the same as that of the dispersion compensating fiber. Then, an end portion of the intermediate optical fiber having been spliced to the single mode optical fiber is heated so that the MFD thereof can be increased to become the same as that of the single mode optical fiber.
It is an object of the present invention to provide a method for connecting optical fibers having different MFDs with a low connection loss.
In order to achieve this object, according to one aspect of the present invention, a method for connecting optical fibers includes the steps of preparing a third optical fiber having a short length and whose MFD is smaller than that of a first optical fiber and larger than that of a second optical fiber; connecting the first optical fiber to the third optical fiber; connecting the second optical fiber to the third optical fiber; and increasing at least one of the MFD of the third optical fiber near the part connected or to be connected to the first optical fiber and the MFD of the second optical fiber near the part connected or to be connected to the third optical fiber by heating the corresponding part.
In the present invention, xe2x80x9can optical fiber having a short lengthxe2x80x9d means such a fiber having a length of about 0.1 through 10 m, and is not for extending the length of a transmission line.
The step of increasing the MFD may be performed before or after the steps of connecting the first optical fiber to the third optical fiber and connecting the second optical fiber to the third optical fiber.
Another method for connecting optical fibers is also proposed that includes steps of preparing a third optical fiber having a short length and an MFD smaller than that of the first optical fiber; increasing the MFD of the third optical fiber near the part to be connected to the first optical fiber by heating the corresponding part; and connecting the first optical fiber to the third optical fiber, and the third optical fiber to the second optical fiber in that order.
The above and further objects and novel features of the present invention will be more fully clarified from the following detailed description when the same is read in connection with the accompanying drawings. It is to be expressly understood, however, that the drawings are for the purpose of illustration only and are not intended as definitions of any limit of the invention.